The present invention relates to a turbine engine. In particular, the invention relates cooling turbine airfoils in a gas turbine engine.
A turbine engine ignites compressed air and fuel to create a flow of hot combustion gases to drive multiple stages of turbine blades. The turbine blades extract energy from the flow of hot combustion gases to drive a rotor. The turbine rotor drives a fan to provide thrust and drives a compressor to provide a flow of compressed air. Vanes interspersed between the multiple stages of turbine blades align the flow of hot combustion gases for an efficient attack angle on the turbine blades.
Rotors and vanes each typically include an airfoil and at least one platform from which the airfoil extends. Combustion gases flowing past airfoils tend to form vortices at the platform surface. Such vortices waste useful energy and reduce the efficiency of the turbine engine. Turbine engines may include rotor or vane airfoils that are curved or bowed to improve the efficiency of the turbine engine by directing the combustion gases away from platforms at the ends of the airfoils, thereby reducing the vortices.
Rotor and vane airfoils are exposed to high-temperature combustion gases and must be cooled to extend their useful lives. Cooling air is typically taken from the flow of compressed air. A portion of the cooling air passes through and cools the airfoil before discharging through cooling discharge openings at a trailing edge of the airfoil. The cooling air discharging from these openings cools the trailing edge. Airfoil trailing edges are made as thin as practical for improved aerodynamic efficiency. Such thin trailing edges limit the cross-sectional area available at the trailing edge for cooling discharge openings. Thus, turbine airfoils may have cooling discharge openings at the trailing edge that extend from the trailing edge along a pressure side of the airfoil. Such pressure side biased cooling discharge openings provide the increased area necessary for the thin trailing edge to receive sufficient cooling air.